1. Field of the Invention
The present invention relates to a process for purifying hydrofluoropropanes of olefinic and saturated chlorinated impurities by concurrent contact with hydrogen and hydrogen fluoride in the presence of a bifunctional catalyst capable of catalyzing hydrogenation and fluorination.
2. Description of Related Art
Hydrofluoropropanes such as 1,1,1,2,3,3,3-heptafluoropropane (CF3CHFCF3, HFC-227ea), 1,1,1,3,3,3-hexafluoropropane (CF3CH2CF3, HFC-236fa) and 1,1,1,3,3-pentafluoropropane (CF3CH2CHF2, HFC-245fa) find application as fire extinguishants, propellants, refrigerants, blowing agents and solvents. Olefins and saturated chlorinated compounds are often present in product streams obtained from hydrofluoropropane manufacture. Removal of these undesirable impurities from hydrofluoropropanes by distillation is often difficult due to similar boiling points or the formation of azeotropes between impurities and hydrofluoropropanes. The presence of such impurities in hydrofluoropropanes is undesirable because they are frequently toxic as well as reactive resulting in unacceptable utility of such impure hydrofluoropropanes in most applications.
U.S. Pat. No. 5,463,152 discloses a process for the hydrogenolysis of a saturated halocarbon in the presence of a palladium on trivalent chrome oxide catalyst and an acid of the formula HZ (wherein Z is Cl, Br or F). U.S. Pat. No. 5,569,797 discloses a process for preparing a hydrochlorofluorocarbon essentially free of olefinic impurities by selectively hydrogenating the olefinic impurities in the presence of a supported or unsupported group VIII metal hydrogenation catalyst. U.S. Pat. No. 5,001,287 discloses a process for treating a mixture of olefinic impurity and saturated halocarbon by contacting the mixture with hydrogen in the presence of a supported or unsupported group VIII metal hydrogenation catalyst. U.S. Pat. No. 6,147,267 discloses a process for recovering a perfluorocycloalkane from a mixture comprising perfluorocycloalkane, an olefinic impurity, and optionally a saturated chlorinated impurity by contacting the mixture with hydrogen in the presence of a hydrogenation catalyst and separating the perfluorocycloalkane from the saturated impurity thereby produced. U.S. Pat. No. 5,208,396 discloses a process for producing saturated halocarbons by reacting saturated or olefinic compounds with hydrogen in the presence of iodine and hydrogen iodide.
The prior art discloses separate processes for removal of olefinic and chlorinated impurities from fluorocarbons that involve separate steps as well as disparate reaction conditions, reagents and catalysts. Such multi-step processes are resource intensive, less effective at producing fluorocarbon substantially free of such impurities and suffer yield loss leading to overall inefficient removal of such impurities. The present invention offers a less resource-intensive process that produces hydrofluoropropanes substantially free of olefinic and saturated chlorinated impurities in high yield by subjecting an impure hydrofluoropropane concurrently to hydrogenation with hydrogen and fluorination with hydrogen fluoride in the presence of a bifunctional catalyst.